Known processes for producing sucrose fatty acid polyesters include a microemulsion method (a solvent-free method) and a solvent method.
In the microemulsion method wherein an alkaline soap is used as a melting agent, a large amount of an alkaline catalyst, compared with the starting sucrose, is added in order to proceed the reaction. However this method is disadvantageous in that the addition of such a large amount of an alkaline catalyst would induce a side reaction between a fatty acid alcohol ester and the alkaline catalyst to thereby form a large amount of a soap, in addition to the desired transesterification products. This reaction should be essentially carried out at a high temperature, which causes the above-mentioned problem. The high reaction temperature further causes a serious coloration of the sucrose fatty acid polyester products.
In contrast thereto, the solvent method comprises reacting sucrose with a fatty acid lower alcohol ester(s) several times by mol as much as said sucrose in a solvent in the presence of a catalyst. In this case, the reaction can be conducted in the solvent under mild conditions and thus the obtained sucrose fatty acid polyester is superior in qualities to the one produced by the solvent-free method.
The solvent method enables the production of a sucrose fatty acid polyester of relatively excellent qualities. In particular, the sucrose fatty acid polyester product obtained by the solvent method contains less alkaline metal components such as fatty acid alkaline soaps than the one obtained by the solvent-free method does. However there has been known no method for economically removing a small amount of the alkaline metal components contained in the former product.
Even in the case of the solvent method, it is required to use a decolorizer in order to give a sucrose fatty acid polyester having a low color value and excellent qualities, which brings about some industrial problems such as a decrease in the yield of the product.
Furthermore, there has been known no method for recovering and reusing the alkaline catalyst in the production of a sucrose fatty acid polyester by the solvent method.